The present invention relates to a method for curing defects in a semiconductor layer.
The SMARTCUT® method is widely employed in the methods for fabrication of semiconductor structures, for transferring a layer from a substrate referred to as donor to a substrate referred to as receiver.
Generally speaking, this method comprises a step for implantation of ion species into the donor substrate.
The implantation profile in the donor substrate is of the Gaussian type, with a peak in a plane corresponding to a plane at a certain depth with a maximum of implanted species, forming a fragilization region or embrittlement zone in the donor substrate.
The layer to be transferred is bounded between the surface of the donor substrate through which the implantation has been carried out and the fragilization region. The SMARTCUT® method subsequently comprises a step for assembling the donor substrate with the receiver substrate, the layer to be transferred being brought into contact with the receiver substrate. Then mechanical, thermal or other forces are applied in such a manner as to fracture the donor substrate along the fragilization region. The remainder of the donor substrate, which could be recycled and re-used, and the final semiconductor structure that comprises the receiver substrate and the transferred layer are separated.
After the transfer, however, defects are present in the transferred layer. These defects are the result of the implantation and formation of the fragilization region, as well as due to the fracture that has been carried out on the donor substrate. These defects can typically comprise defects in the crystal lattice of the transferred layer, together with residues of the implanted species, etc. Such defects are capable of altering the operation of the electronic devices formed in or on the transferred layer.
In order to cure these defects, a known solution is to apply to the semiconductor structure thus formed a thermal treatment at a high temperature. In this respect, reference is made to the U.S. Pat. No. 6,403,450, which describes a method for curing post-fracture defects that comprises an oxidation of the surface of the transferred layer followed by a thermal treatment at a temperature of around 1100° C. There are situations, however, in which it is not possible to apply a thermal treatment at such a high temperature. This is notably the case when the receiver substrate is a substrate having been previously processed so as to comprise electronic devices, interconnections, metallized regions, etc., which would be altered by the application of a thermal treatment at a high temperature, in other words, greater than around 500° C. This is also the case when the transferred layer itself cannot be exposed to high temperatures, such as, for example, when this layer comprises a PN junction that would be damaged if it were exposed to temperatures exceeding 800° C. (owing to the diffusion of the dopants in the layers forming the junction).
U.S. Patent Publication No. 2005/0280155 discloses one example of a method in which a semiconductor layer comprising a PN junction is transferred onto a receiver substrate comprising electronic devices and an interconnection region comprising metallized portions, where the transfer of the semiconductor layer may be carried out by the SMARTCUT® method. Such a receiver substrate must not be exposed to a high temperature. Thus, the application of a thermal treatment at a lower temperature, in other words, lower than around 500° C., or the application of conditioning processing steps not implementing any thermal treatment (polishing, etc.), so as to avoid damaging the receiver substrate, might not be sufficient to cure all of the defects in the transferred layer. This insufficient or incomplete curing of the defects compromises the operation of devices formed later on in or on the transferred layer. In particular, since the implantation notably has the effect of de-activating certain types of dopants, the PN junction that it contains risks no longer being operational.
The aim of the present invention is to overcome these problems and, more particularly, to provide a method for curing defects due to the implantation into the transferred layer, which does not risk damaging the receiver substrate, whatever the devices or functions present in the receiver substrate.